The following description of general background of the present invention makes reference to drawing figures including FIGS. 1 through 4. The combustion process of coal in power utility fired boilers produces two types of waste products: 1) ash particles that are small enough to be entrained in the flue gas referred to as fly ash, and 2) relatively large ash particles that overcome drag in the combustion gases and drop to the bottom of the boiler referred to as bottom ash. Typically, bottom ash is either collected in a water impoundment or in a dry bottom. Water impounded ash, referred to as wet bottom ash, is typically collected in individual water filled hoppers, as shown in FIG. 1 which illustrates a typical bottom ash to pond system 10, or in a closed loop recirculation system 26 shown in FIG. 2, or in a water filled trough with a submerged drag chain system 12 as shown in FIG. 3. In the system of FIG. 1, ash is discharged each shift in a batch process from hoppers 14 through a bottom gate 16 on the side of the hoppers 14. Grinders 18 are provided to reduce ash particle size to less than 2 inches (typically) to allow conveyance in a pipe as an ash/water slurry. The slurry is discharged into a storage pond 20 where the ash settles out over time. Numerous pumps 22 and valves 24 are provided for moving the slurry through system 10. A modified form of system 10 provides closed loop dewatering system referred to as “Hydrobin® Dewatering System” 26 as shown in FIG. 2.
In the system 26 shown in FIG. 2, bottom ash 11 is discharged from the hopper 14 into the grinder 18 and is then pumped to remotely located dewatering bins 28. There is provided a two-stage settling process which is necessary to clarify the water enough for recycling. Settled ash is drained of water through screens in the dewatering bins 28. Surge tank 30 and settling tank 32 handle the drained water and provide further clarification and separation of coal ash from the water. Clarified water is recycled back to convey the next batch of ash slurry. Dewatered ash slurry is hauled away from the plant site.
The submerged mechanical drag conveyor system 12 illustrated in FIG. 3 is typically applied to provide continuous ash removal. Ash from the submerged drag chain conveyor unit 34 is dewatered through an inclined section 36 and transported via a conveyor 44 and into a bottom ash silo 38 and is discharged into a truck to transport the material off-site. Mill reject hoppers 40 are provided to process such material which is directed onto chain conveyor inclined section 36 for processing along with the bottom ash slurry stream. The submerged drag chain conveyor unit 34 is positioned directly beneath the boiler ash hopper discharge 42. Another view of submerged drag chain conveyor unit 12 is shown in FIG. 4 which further illustrates the conveyor drive unit 46 and take-up unit 48 which provides proper conveyor chain tensioning. In this prior art system, one of the units 12 shown in FIGS. 3 and 4 is provided for each boiler ash hopper discharge 42. In the unit of FIG. 4 the dewatered ash is directly discharge into a truck for off-site transfer.